THE WHITE BLOOD-CELLS. These are notch fewer in number than the red cells, the average being about one white cell to every four or five hundred of the red. The proportion, however, varies. They are slightly larger than the red cells, about to 10 micromillimeters in diameter. Their shapa varies, largely from their anueboid movement. They are nucleated, and the protoplasm of the cell-body is more or less granular. Several varieties of the white blood-cell are recognized, which may be classi fied as follows: (1) Lymphocytes, large and small, halloo' a round nucleus surrounded by a small rim of cell-body; and (2) LcucomiteR, which may be further subdivided into large mononuclear leueoeytes, in which there is round or oval nucleus with considerable cell-body; transitional forms. in which the nuclei are ir regular in shape; polynuclear leueoeytes, in which there are several nuclei. and eosinophile leucocytes, which have in their cell-bodies large granules which stain bright red with eosin. The
ameeboid movement of the white cells enables them to change their shape and to accomplish some locomotion. In this way they pass through the walls of the capillaries into the tissues, where they are known as wandering cells. (See Cox NEcnvE TISSUE.) The blood-platelets are small, non-nucleated, round or oval bodies, about one third the diameter of a red blood-corpuscle. They are found usually in groups and are prone to dis integration. Their function is unknown, but there is reason for believing that they are con cerned in the process of coagulation when it oc curs. Embryologically the white blood-cells are derived. like the red cells, from the mesoblast. In the adult, new white cells are derived by re production. This reproduction seems to occur largely in the lymphatic organs, especially the spleen.